1. Field of the Invention
The present invention relates to a tunable filtering device for optical communications, and more particularly, to a tunable filtering device for optical communications which can transmit a beam of a selected specific wavelength from a beam of multiple wavelength signals.
2. Description of the Related Art
In optical communications, to increase the data transmission quantity per unit time, a plurality of signals having different wavelengths which do not interfere with each other are transmitted through a single optical fiber. By doing so, communication can be performed using not only fewer communication systems as a whole, but also using fewer communication lines.
In optical communication which uses a plurality of signals of different wavelengths, it is necessary to selectively receive or detect only a signal of a specific wavelength at the receiving side, in most cases. In this case, a tunable filtering device is used to selectively transmit a beam of a specific wavelength.
Such a tunable filtering device for optical communications may be used in optical communication systems employing a wavelength division multiplexer (WDM), erbium-doped fiber amplifiers (EDFAs), or the like.
As shown in FIG. 1, a prior tunable filtering device for optical communications comprises a tunable filter unit 10 and a tap unit 30 which are installed on a first base 1 and a second base 2, respectively. The tunable filter unit 10 transmits a beam of a specific wavelength from an incident beam of various wavelengths, and the tap unit 30 splits the beam transmitted through the tunable filter unit 10, providing one of the split beams to control the tunable filter unit 10 and the other as the output.
The tunable filter unit 10 includes a line filter 20 for selectively transmitting a beam of a specific wavelength from the beam incident from a first optical fiber 11 toward a second optical fiber 13, and an actuator 15 for controlling the position of the line filter 20.
A first lens 21 collimates a divergent beam and is installed at the output side of the first optical fiber 11, and a second lens 23 converges a collimated beam from the line filter 20 and is installed at the input side of the second optical fiber 13.
The line filter 20 transmits a beam of a predetermined wavelength according to an angle between the line filter 20 and the collimated beam incident thereon. Accordingly, a beam of a specific wavelength desired to be transmitted can be selected by controlling the angle of the line filter 20 with respect to the collimated incident beam, using the actuator 15.
The tap unit 30 includes a third optical fiber 35 to which the signal beam from the second optical fiber 13 is transferred, a beam splitter 40 for both transmitting and reflecting the incident beam from the third optical fiber 35, a fourth optical fiber 37 for transferring the beam reflected from the beam splitter 40 to a controller (not shown) which controls the actuator 15, and a fifth optical fiber 39 for transferring the beam transmitted through the beam splitter 40.
The third optical fiber 35 is connected to the second optical fiber 13 by a connector 25, and a third lens 45 which collimates a divergent beam is installed at the output side of the third optical fiber 35. A fourth lens 47 which converges the collimated beam reflected from the beam splitter 40 is installed at the input side of the fourth optical fiber 37, and a fifth lens 49 which converges the collimated beam transmitted through the beam splitter 40 is installed at the input side of the fifth optical fiber 39.
The actuator 15 is driven by the controller according to a detection signal of the beam transmitted through the fourth optical fiber 37. In other words, the angle of the line filter 20 relative to the incident beam can be decided by measuring the amount of the beam the received by an optical detector of the controller. Consequently, the tunable filtering device can transmit only a signal beam of a desired specific wavelength by controlling the angle of the line filter 20.
However, in the prior tunable filtering device, since the tunable filter unit 10 and the tap unit 30 for splitting the incident beam to control the tunable filter unit 10 are separately installed on different bases, the connector 25 for interconnecting the two units 10 and 30 is requisite. Further, since a plurality of lenses and fibers are required, optical alignment between them is difficult, the construction of the device is complicated, and therefore the various optical losses are increased.